As it becomes possible to fit more and more circuit elements onto a single substrate, a correspondingly larger number of interconnects may be fabricated on the substrate to connect the circuit elements to off-substrate circuitry. Conventional interconnects are often formed on the same side of the substrate as the circuit elements (the xe2x80x9cfrontsidexe2x80x9d of the substrate), and terminate at contact pads formed around the perimeter of the substrate frontside. With each increase in the number of circuit elements on a single substrate, the contact pads and interconnects often become more crowded around the perimeter of the substrate. Sometimes the size of the interconnects are reduced to squeeze them into the available space. The reduced interconnect size may lead to various problems, such as a high interconnect resistance caused by the small cross-sectional area of the interconnects, as well as increased manufacturing costs due to the increased miniaturization.
In various specific implementations, the placement of interconnects on the substrate frontside may cause other problems as well. For example, interconnects that connect the firing mechanisms in a printing device printhead die to external circuitry are often formed on the same side of the substrate as the fluid ejection nozzles. Thus, these interconnects may be exposed to printing fluids during printhead use, which may damage the interconnects and lead to the eventual failure of the printheads. Furthermore, due to the thickness of the encapsulent beads used to electrically insulate and protect the interconnects, the printhead may be positioned at such a distance from a printing medium that droplets of printing fluid ejected from the printhead may spread an unfavorable amount before reaching the printing medium. Excessive spreading of printing fluid droplets may make precision printing more difficult.
Some embodiments provide a method of fabricating a through-substrate interconnect for a microelectronics device, the device including a substrate having a frontside and a backside. The method includes forming a circuit element on the frontside of the substrate, forming a trench in the backside of the substrate that extends to the circuit element, forming a layer of an insulating polymeric material in the trench, removing sufficient polymeric material from the layer of the insulating polymeric material to at least partially expose the circuit element, and forming an electrically conductive interconnect layer in the trench, wherein the interconnect layer is in electrical communication with the circuit element.